mac80211: request TX status where needed

Right now all frames mac80211 hands to the driver
have the IEEE80211_TX_CTL_REQ_TX_STATUS flag set to
request TX status. This isn't really necessary, only
the injected frames need TX status (the latter for
hostapd) so move setting this flag.

The rate control algorithms also need TX status, but
they don't require it.

Also, rt2x00 uses that bit for its own purposes and
seems to require it being set for all frames, but
that can be fixed in rt2x00.

This doesn't really change anything for any drivers
but in the future drivers using hw-rate control may
opt to not report TX status for frames that don't
have the IEEE80211_TX_CTL_REQ_TX_STATUS flag set.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com> [rt2x00 bits]
Signed-off-by: John W. Linville <linville@tuxdriver.com>